Thats because it was planned to go into production before WB knew the response to BvS and that’s why they aren’t doing anything like that ever again.
I’m aware it did well worldwide, but again if it was such a hit why didn’t WB sign up Ayer for the sequel right away?
I don't know why you're using the term "if" it's such a hit. You just said you're aware that it did well worldwide, it's an objective fact.
So I take that you do acknowledge it did fantastic in the USA right? 325M better than Deadpool 2+Xmas edition, and better legs than Civil War
and like you just said, they f***ed themselves with the JL schedule and eventually the reshoot, so WB or at least the Hamada team knows that if you take a critically panned movie that made a lot of money (other examples - TF) and make a sequel with the same director (still credited ZS) and gets another s***y score, and same characters it's game over.
So using the breakout character/actress who just got nominated for an Oscar in 2018 and put her in a different team and brand it as the first ever female team up movie with a female director and low budget is their way of retaining the audience from a movie that made 745M worldwide and ensure they don't repeat JL's situation of getting crappy RT and negative press from the director's name.
Other reasons for the sequel/spin off delays could be because Will and Margot are busy, JL underperformed so they need to re-think their plan and slow down, Ayer's probably not happy, and possibly O'Connor's story got stolen by BOP so they need another guy to come in and restart the whole thing again.
But it's not like they wait 5 years and make one spin off and call it a day. They are making a direct sequel plus a whole bunch of others with Harley, you only do that if you have some sort of a hit you know.